Would you be interested in supporting PlaceholderAPI in this API? It seems like you have a foundation for different types of texts in sidebars and items so a PlaceholderText type of object might be useful. I can understand wanting to minimize dependencies so if you don’t want to add this it’s fine (PlaceholderAPI tries to minimize as well).
If you want I can create a PR that adds basic support (though you may want to add more complicated support later) to help this process along.